I think it probably depends on your building. Are you locating in a city or a rural area?
I'd probably ask my builder for some options initially. Is it attached to your house or set away?
How is your house heated? Could you extend the system into the garage or does it have to be a completely seperate system? Do you have solar panels on the garage roof?
Will you need to think about keeping it cool in the summer?
Electricity is more expensive in Ireland compared to the UK so I'd be wary of using just an electric form of heating myself.
I just use a calor gas fire I find it way better than electric heaters, it's super cold in my salon because we're facing away from the sun so even in the middle of summer it's blinkin freezing! I put the fire on first thing when I come in onto number 2 then turn it down when people come in, not one person has been cold this winter thank god lol, last year was awful before I got the fire, clients were litterally shivering some days! Problem solved now tho!
My first salon was above a shop, the building was over 100 yrs old and was their living quarters back in the day so no heating was ever installed.
I had oil radiators plugged them into a timer switch so they came on half hr before I got in and went off half hr before I left.
As they had their own thermostats they happily switched on and off all day themselves. It was lovely and warm
I dreaded the electric bill the first winter quarter but was pleasantly surprised how little they used.